2,378 research outputs found

    Interferometric Astrometry of Proxima Centauri and Barnard's Star Using Hubble Space Telescope Fine Guidance Sensor 3: Detection Limits for sub-Stellar Companions

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    We report on a sub-stellar companion search utilizing interferometric fringe-tracking astrometry acquired with Fine Guidance Sensor 3 (FGS 3) on the Hubble Space Telescope. Our targets were Proxima Centauri and Barnard's Star. We obtain absolute parallax values for Proxima Cen pi_{abs} = 0.7687 arcsecond and for Barnard's Star pi_{abs} = 0.5454 arcsecond. Once low-amplitude instrumental systematic errors are identified and removed, our companion detection sensitivity is less than or equal to one Jupiter mass for periods longer than 60 days for Proxima Cen. Between the astrometry and the radial velocity results we exclude all companions with M > 0.8M_{Jup} for the range of periods 1 < P < 1000 days. For Barnard's Star our companion detection sensitivity is less than or equal to one Jupiter mass for periods long er than 150 days. Our null results for Barnard's Star are consistent with those of Gatewood (1995).Comment: 35 pages, 13 figures, to appear in August 1999 A

    Ectoplasm & Superspace Integration Measure for 2D Supergravity with Four Spinorial Supercurrents

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    Building on a previous derivation of the local chiral projector for a two dimensional superspace with eight real supercharges, we provide the complete density projection formula required for locally supersymmetrical theories in this context. The derivation of this result is shown to be very efficient using techniques based on the Ectoplasmic construction of local measures in superspace.Comment: 18 pages, LaTeX; V2: minor changes, typos corrected, references added; V3: version to appear in J. Phys. A: Math. Theor., some comments and references added to address a referee reques

    Photometry of Proxima Centauri and Barnard's Star Using HST Fine Guidance Sensor 3: A Search for Periodic Variations

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    We have observed Proxima Centauri and Barnard's Star with Hubble Space Telescope Fine Guidance Sensor 3. Proxima Centauri exhibits small-amplitude, periodic photometric variations. Once several sources of systematic photometric error are corrected, we obtain 2 milli-magnitude internal photometric precision. We identify two distinct behavior modes over the past four years: higher amplitude, longer period; smaller amplitude, shorter period. Within the errors one period (P ~ 83d) is twice the other. Barnard's Star shows very weak evidence for periodicity on a timescale of approximately 130 days. If we interpret these periodic phenomena as rotational modulation of star spots, we identify three discrete spots on Proxima Cen and possibly one spot on Barnard's Star. We find that the disturbances change significantly on time scales as short as one rotation period.Comment: 39 pages, 17 figure

    Becoming an older volunteer: A grounded theory study.

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    This Grounded Theory study describes the process by which older persons “become” volunteers. Forty interviews of older persons who volunteered for Habitat for Humanity were subjected to secondary content analysis to uncover the process of “becoming” a volunteer. “Helping out” (core category) for older volunteers occurs within the context of “continuity”, “commitment” and “connection” which providemotivation for volunteering.When a need arises, older volunteers “help out” physically and financially as health and resources permit. Benefits described as “blessings” of volunteering become motivators for future volunteering. Findings suggest that older volunteering is a developmental process and learned behavior which should be fostered in older persons by personally inviting them to volunteer. Intergenerational volunteering projects will allow older persons to pass on knowledgeand skills and provide positive role modeling for younger volunteers

    Eleven-dimensional massless superparticles and matrix theory spin-orbit couplings revisited

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    The classical probe dynamics of the eleven-dimensional massless superparticles in the background geometry produced by N source M-momenta is investigated in the framework of N-sector DLCQ supergravity. We expand the probe action up to the two fermion terms and find that the fermionic contributions are the spin-orbit couplings, which precisely agree with the matrix theory calculations. We comment on the lack of non-perturbative corrections in the one-loop matrix quantum mechanics effective action and its compatibility with the supergravity analysis.Comment: 11 pages, Latex, no figure

    Darboux Transformations for Supersymmetric Korteweg - de Vries Equations

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    \hspace{.2in}We consider the Darboux type transformations for the spectral problems of supersymmetric KdV systems. The supersymmetric analogies of Darboux and Darboux-Levi transformations are established for the spectral problems of Manin-Radul-Mathieu sKdV and Manin-Radul sKdV. Several B\"acklund transformations are derived for the MRM sKdV and MR sKdV systems.Comment: Latex, 8 pages AS-ITP-94-4

    ADOLESCENT AMENORRHEA

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    Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73937/1/j.1749-6632.1967.tb14694.x.pd

    On A Superfield Extension of The ADHM Construction and N=1 Super Instantons

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    We give a superfield extension of the ADHM construction for the Euclidean theory obtained by Wick rotation from the Lorentzian four dimensional N=1 super Yang-Mills theory. In particular, we investigate the procedure to guarantee the Wess-Zumino gauge for the superfields obtained by the extended ADHM construction, and show that the known super instanton configurations are correctly obtained.Comment: 22 pages, LaTeX, v2: typos corrected, references adde
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